1. Field of the Invention
The invention relates to a heat exchanger for the transmission of heat produced in a gas cooling circuit of a high temperature reactor to a gas circulating in an intermediate circuit for further use in a process heat plant. The heat exchanger is arranged in a pod within the reactor pressure vessel.
2. Description of the Prior Art
German Offenlegungsschrift No. 21 20 544 illustrates a heat exchanger for use in closed gas turbines. The heat exchanger has a number of tube bundles which are arranged in parallel and which have a round or polygonal cross-section. The bundles are surrounded by tubular casings which are open at both ends. The external heat exchanger medium, e.g. the waste gas coming from a turbine, flows within these casing tubes along the exchanger tubes such that its direction of flow is countercurrent to the flow of the medium in the tubes. Each tube assembly is provided with its own supply and removal lines. The casing tubes are inserted in a sealed and leakproof manner in a plate arranged horizontally to them, which is partially connected to the housing of the heat exchanger at its sealed portion.
A similar heat exchanger having tube assemblies surrounded by guide casings is described in the German Offenlegungsschrift No. 24 30 161. The tube assemblies designed as boxes are arranged in planar form in a hexagonal grating. The tube bottoms are arranged at least at one side in different horizontal planes. The heat exchanger is particularly suitable for use as a recuperator in the cooling circuit of a high temperature reactor having a helium-turbine. When used as such, it is arranged in a cavity in the wall of a prestressed concrete vessel. In the event the heat exchanger is to be suspended within the cavity, the boxes are suspended by means of thermo sleeves onto a supporting grate, which is partially mounted on the liner of the pod by means of a thermo sleeve. When used in a stationary arrangement, the heat exchanger rests on a supporting grate at the seam of an external ring and six spokes.
Furthermore, German Offenlegungsschrift No. 24 59 189 teaches a tube-bundle type of heat exchanger for gaseous medium, which also forms a part of a fully integrated nuclear reactor plant having a helium-turbin. The type bundles have a ring-shaped cross-section, and their collectors and distributors are designed as ring-shaped chambers. The distributors are connected across the supply lines through a spherical bottom which serves as a main distributor, as well as a supporting grate. The supply lines are fixed connected to the spherical bottom. The removal lines are led as compensating loops along the circumference of the heat exchanger upwards to a ring collector, at which place they penetrate the spherical bottom.
Additionally, one prior art recognized design of a nuclear power plant has a closed gas cooling circuit for the production of process heat, wherein a primary circuit and an intermediate circuit are arranged, so as to separate the heat exchanger to a high temperature part and a low temperature part. Both the high temperature part and the low temperature part are removably installed in separate pods within the prestressed concrete vessel. The reason for this particular arrangement is based on the fact that the high cooling-gas temperatures necessary for the purpose previously indicated only occur in the area of the gas inlet of the heat exchanger. Therefore, it is sufficient to provide only the high temperature portion of the heat exchanger with high resistance material capable of exhibiting a long service life. Since both heat exchanger parts are arranged in separate pods, the portion exposed to stress can be removed and separately replaced. Nevertheless, the splitting up of the heat exchanger into separate parts connected in series is done at the expense of the stability and structural integrity of the entire nuclear power plant.
It is, therefore, most desirable to construct heat exchangers for the removal of heat produced in high temperature reactors which are as compact as possible and convenient for integration into the prestressed reactor vessel for reasons of technical safety. Furthermore, the heat exchanger must be gas-tight even under extreme pressure differences which may arise as a result of accidental distrubances, that is, no radioactively contaminated coolant may be permitted to enter the intermediate circuit. Since for reasons of efficiency, it is also necessary that the heat be introduced into an ongoing process (e.g. coal gasification) which is effected at high temperatures (approx. 900.degree. C.), there are great problems with respect to the choice of suitable materials for the construction of the heat exchanger. The material used should be able to provide as long a service life as possible at the high temperatures discussed (the service life of the plant is approximately 30 years). Also, the metal components utilized as discussed above have only very small strength factors at such temperatures, therefore, their demands are limited.